An elevation of privilege vulnerability exists when the Windows Common Log File System (CLFS) driver improperly handles objects in memory. An attacker who successfully exploited this vulnerability could run processes in an elevated context. To exploit the vulnerability, an attacker would first have to log on to the system, and then run a specially crafted application to take control over the affected system. The security update addresses the vulnerability by correcting how CLFS handles objects in memory.
https://www.tenable.com/blog/tenable-roundup-for-microsofts-june-2019-patch-tuesday
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-0959
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2019-0959